There are instances in which it would be desirable to track and or estimate the location of individual units within a network, including multi-hop and/or ad-hoc networks. In at least some of these instances, some of the more traditional approaches, such as approaches based upon triangulation/trilateration, may be unavailable. For example, for at least some of the units there may be an insufficient number of range measurements relative to one or more reference units, whose locations are known, to enable a unit to be located to be able to determine its location.
However, despite not having a sufficient number of range measurements relative to one or more reference units for any particular one or more units, in some instances a location estimation can be determined based upon a known relationship of a group of units relative to one another, as well as the relationship between at least some of the units in the group relative to one or more reference units. In at least some instances, an iterative approach may exist for estimating a location for a plurality of units forming a multi-hop network. One such example includes Patwari et al., U.S. Pat. No. 6,473,038.
In at least some iterative approaches, the various distance/range information is gathered in a centralized location, where a set of locations are initially estimated, and a corresponding error value is determined for the set of locations. The location estimates will be iteratively adjusted until the corresponding error value is minimized. In at least some instances an error value will be based upon the accumulated differences associated with the distance between units relative to the estimated locations, and the measured distance between units using one or more measured ranging techniques.
However as the number of units in the network increases, the volume of information that needs to be collected at the central unit where the location estimates are to be determined increases. Still further, the distance measured in the number of hops that some of the information will need to travel to be received at the central unit where the location estimates are determined will also often similarly increase as the number of units in the network increases. In some instances, the number of hops can be minimized to the extent that the particular unit where the location estimates are determined is selected as being one of the units located toward the center of the units. Each hop generally introduces a corresponding delay or latency associated with gathering the associated range information at the unit where the location estimates are determined, as well as representing an additional unit that the information needs to travel through in order to be received by the unit where the location estimates are determined.
In addition to delays associated with multiple hops, traffic densities in and around the unit where the location estimates are determined are often heightened and in some instances can result in one or more truffle bottlenecks. Furthermore, this can cause non-uniform energy consumption to occur. Further yet, the location computational time exponentially increases with every additional blindfolded unit (i.e. unit whose location is to be determined) in the network.
The present inventors have recognized that subdividing a plurality of units, whose locations are to be determined, into a plurality of sub-nets can generally be done without adversely affecting the network's ability to determine the location of the units. Furthermore, the determination of the locations of the units can then be distributed between multiple units that are associated with each of the sub-nets.